It seems like every other day a funky new robot arrives on the scene—not surprising, given the current pace of technological advancement and innovation. This means we’re seeing lots of unique bots that are primarily used to explore different types of locomotion, connectivity, programming and structural designs.

A lot of the fun working in robotics comes from the challenge, however, and seeing just how far you can push a given concept. Adding legs to robots is one of these concepts, where creative engineers are building everything from a single-legged robot that can jump like a pogo-stick, to two-legged robots that walk like humans, to four-legged and six-legged robots that can move like animals and insects.

The addition of more legs makes a robot more stable, able to move more naturally, and lets them tackle complicated terrain. Following the “more legs is better” philosophy eventually leads to a robot like the Mochibot, a spherical robot that uses 32 individually actuated telescoping legs to move around.

(Image courtesy of Keio University/University of Tokyo.)

Mochibot was developed by a team of roboticists from Keio University and the University of Tokyo. While a robot capable of omnidirectional movement would ideally be spherical, a sphere is inherently unstable because there is only a single contact point between the object and the ground. Therefore, their design for Mochibot is only mostly spherical, with a shape based on a rhombic triacontahedron—a polyhedron with 32 vertices and 30 faces in the shape of rhombuses.

The telescoping legs on Mochibot make it deformable, adjusting the amount of ground contact it has in order to move around. Movement occurs by retracting arms in the direction of motion, while extending the arms on the opposite side, and flattening itself parallel to the ground in order to stop.

Each leg is individually telescoping, with a design featuring three sliding rails that act like linear actuators. The legs can extend to a little less than two feet, or retract to just under twelve inches. During operation, the legs don’t quite stretch to the full extent, making the maximum diameter of Mochibot approximately one meter (three feet), with the minimum diameter measuring about half a meter. Including all the hardware and batteries, the bot weighs in at 10 kilograms. Although the current version of the robot doesn’t have built-in payloads, there is space for additional equipment such as sensors or cameras both inside the body and on the arms.

(Image courtesy of NASA.)

The idea for a deformable, squishy-structured robot isn’t new; NASA has been working on a tensegrity robot for some time, with hopes that one day it could be used to explore other planets and moons, such as the surface of Titan. Tensegrity structures consist of rigid components such as hollow, cylindrical rods, connected by an elastic and stretchable material, such as elastic cables.

Dubbed the Super Ball Bot, NASA’s tensegrity robot is a bit more robust and deformable than Mochibot in some respects. It’s even capable of surviving a fall from a roof. However, the Super Ball Bot isn’t able to achieve a nearly spherical form, and the locomotion machine learning algorithms are extremely complex to achieve motion that is essentially the bot flopping over itself. It’s also difficult to steer, which is a distinct disadvantage in planetary exploration, where a robot needs to go precisely where it’s been directed.

This is where Mochibot holds the advantage over a tensegrity robot. Since each leg is extendible and retractable, the bot can move smoothly and continuously in any direction. Mochibot is better at moving over terrain such as sand or loose rocks because rolling movement doesn’t depend on traction. This also gives Mochibot a ‘leg up’ on wheeled exploration concepts, which operate best on relatively smooth, obstacle-free surfaces with high traction.

Some of the biggest success stories in planetary exploration are NASA’s rovers—Spirit, Opportunity and Curiosity—but even these expeditions haven’t been problem-free when navigating the Martian surface. Over the years, the rovers have experienced damaged wheels, terrain too rocky or unstable to drive on, and getting stuck in sand or crevices.

Having 32 independently operating legs offers a high level of redundancy. If something goes wrong with one leg, there are many others still operational and able to continue the robot’s movements.

This combination of advantages—high mobility, redundancy and room for science payload—make Mochibot extremely versatile and ideal for applications including disaster response and planetary exploration. Next up for the team is experimenting with movement over different terrain types to see how Mochibot handles environments similar to extraterrestrial surfaces full of rocks, slopes and gullies.

Maybe someday, we’ll see Mochibot—or a robot like it—sent off to explore distant terrestrial and extraterrestrial locations.

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